Process for the manufacture of



Patented Nov, 21, 1934 UNITED STATES rnocnss non THE MANUFACTURE ACETIC ACID FROM ACETALDEHYDE Karl Wiesler, Constance, Germany, assignor, by mesne assignments, to the firm of Deutsche Goldund Silber- Scheideanstalt vormals Roessler, Frankfort-on-the-Main, G

ermany No Drawing. Application January 27, 1930,

1855a! No. 423,900. In Germany February 26, I

12 Claims. (c1. zoo-116) a It has been known for along time that acetaldehyde can be oxidized to acetic acid by the action of air see Liebig A. 14, 139). In carrying out this reaction in practice great difficulties are caused as by the absorption of oxygen in acetaldehyde, first unsuitable intermediate products (either peracetic acid (CHaCOODH) or acetaldehyde peroxide (CH3CHO.O2)) are formed. The conversion of these intermediate products into acetic acid takes place very vigourously. In treating large quantities dangerous explosions can, therefore, occur. For this reason various proposals have already been made to enable the oxidation of acetaldehyde to acetic acidto be carried out on the commercial scale in a nondangerous manner. Thus, for example, it has been proposed to add catalysts whose presence accelerates the decomposition of the peracetic acid. -A further proposal consists in that by the use of relatively high temperatures (about 100 C.) the dangerous accumulation of peracetic acid is counteracted, which precaution meanwhile en tails the diminution of the yield (an increase in the formation of carbon dioxide), and furthermore is not absolutely reliable as, with accidental lowering of the temperature the peracetic acid is not destroyed.

It has been found that a dangeroua accumulation of peracetic acid can be avoided with security, and the oxidation of acetaldehyde to acetic acid on the commercial scale can be carried out in a simple and smooth manner if an excess of oxygen, or oxygen admixed with inert gases is used, such that the quantity of oxygen considerably exceeds the quantityof oxygen required for the oxidation of the acetaldehyde to acetic acid.

The process can, for example, be carried out in such a manner that acetaldehyde is allowed to flow continuously into a mixing vessel and, at

40 the same time, the oxidizing gas or gas mixture, the quantity of which is so measured that the quantity of oxygen added is considerably higher than the quantity theoretically. required for the oxidation of the inflowing acetaldehyde to acetic acid, is led in. Preferably, for example, quantities of oxygen are used which exceed the quantity theoretically required by about per cent tures only a very little carbon dioxide is formed,

so that the formation of acetic acid proceeds with better yields.

When working in apparatus with large average quantities the excess heat of reaction is preferably conducted away by indirect cooling, for example in such a manner that a cooling apparatus is built in, or immersing thewhole mix.- ing vessel in a cooling bath. The production output can be increased by good mechanical mixing. The mixing can, for example, be effected by means of stirrers built into the mixing vessel, or for example in such a manner that acetaldehyde and oxidation gas are passed through turbomixers or other suitable mixing devices, or if desired through several consecutive turbo-mixers.

In using higherpressures the oxidation generally proceeds in the same manner as at atmospheric pressure; on the other hand the acetaldehyde is more completely converted, so that by use of excess pressure, smaller absorption apparatus can be used for recovery of the unaltered acetaldehyde. Also, the absorption of the unaltered 7 acetaldehyde can be improved by theuse of higher pressures. The working pressure does not need to considerably exceed atmospheric pressure. Pressures of about 1.5 atmospheres have been proved to be suitable. With continuous working methods it is preferable to carry outthe procedure in such a manner that the waste gas, after passing the absorption apparatus, is passed through a pressure regulator. The pressure regulation can be carried out in a simple and reliable manner, for example by passing the waste gas from'the bottom into a vessel of the wash-bottle type which is filled with water, to a predetermined height according to the degree of excess pressure desired.

In working in accordance with the invention, the reaction starts immediately. The formation of acetic acid proceedssmoothly and so rapidly that the operation canbe carried out with high average quantities, that is to say in a given anparatus high production yields can be obtained. The peracetic acid concentration never exceeds, as has been found, a few tenths per cent, so that dangerous accumulations of this body are obviated.

The high velocity of flow ensures at the same time particularly favourable reaction conditions, on the one hand that the rapid gas stream extraordinarilyimproves the mixing, and on the other hand that the effective limiting surface between the gas and liquid is particularly large. The process can also be carried out withthe cooperation of oxygen carriers of known type. The reaction-promoting action of the high oxygen concentration, together with the large gas velocity, however enables the treatment of such 'large' working quantities that oxygen carriers can vention, the temperature can be kept unaltered be omitted entirely, but also the addition of particular catalysts for the destruction of the paracetic acid is unnecessary as, as already mentioned, appreciable peracetic acid concentrations do not occur.

A further advantage of the process consists in that the temperatures can be so selected that the most favourable course of reaction is obtained. It is, for example, not necessary (as has been effected in some processes) to keep the'temperature at the beginning of the oxidation below a definite limit by carefully supervised cooling or addition of oxygen and only to allow it to increase gradually. It is also not necessary (as has been effected in other processes) to maintain a high'temperature, likewise to be exactly supervised, in definite parts of the apparatus, in. order to decompose the peracetic acid; Furthermore, in operating accordingto the present induring the whole of the continuous process, so that after once regulating the velocity of flow and the cooling the supervision is extremely simple.

The temperature can thus be so adjusted and kept atsuch a degree as is most favourable for the absorption of oxygen, or for the formation of acetic acid (lower temperatures, as is known, reduce the reaction velocity, that is to say reduce the yield of production whilst higher temperatures again entail too extensive oxidation, and therefore influence the yield).

The large quantity of gas introduced into the process according to the invention also supports the maintenance of the desired reaction temperature, firstly in that the reaction product withdraws direct heat from the vapours introduced with it and, further, that the heat exchange through the walls of the cooling device is favoured by the high gas velocity and the energetic movement of the liquid.

The further treatment of the reaction product can be effected in the usual manner. The liquid reaction product about 95 per cent acetic acid with small contents of acetaldehyde can, for example, besubjected to a rectification whereby, after short running, acetic acid is obtained direct. The waste gases can be passed through cooling and absorbing devices in order to recover the acetaldehyde vapours carried with them. For absorption awash-tower sprinkled with water or acetic acid as a washing liquid, can for example be used. Preferably the crude reaction product is used as an absorption agent. This contains some acetaldehyde; at the low temperatures in the washer it is capable, however, of absorbing still further considerable quantities of acetaldehyde.

The acetaldehyde'residues which then still remain in the waste gas can be washed out with acetic acid freed from acetaldehyde but not rectified, or with water, if desired, with consecutive use of the said absorption agents. lation work is saved by treating in this manner, and the absorption proceeds substantially more simply and more economically. This method of operation also enables the use of suitably large quantities of absorption liquid without thereby incurring increased rectification costs. With the use of large quantities of absorption agents the desired washing action is obtained with a smaller absorption apparatus, which is of greatv advantage for the economy of the process. wash tow- Much distilers with filling bodies, or other gas absorption apparatus can be used as absorption devices.

Examples 1. In a mixing vessel 79.2 kg. of acetaldehyde and 1'70 cu. m. of air were introduced per hour. The mixing vessel was provided with a stirrer and with a cooling coil. The temperature was .maintained at about 70 C. The reaction product was cooled down and partially used for spraying, the absorption towers. The waste gases were cooled, and washed in the absorption tower consecutively with the liquid reaction product, and then with reaction product freed from acetaldehyde, and finally with water. The unaltered acetaldehyde of about 8.3 kg: per hour (10.4% of the quantity used) was recovered from the absorption agent by distillation and again introduced to the oxidation. 4

An acetic acid of about 95% strength was obtained with a yield of 97% of the theoretical amount. The production yield amounted to 2250 kg. of acetic acid daily.

2. In an apparatus the capacity of which was one-twentieth of that used according to Example 1, 10.15 kg. of acetaldehyde and 9 cu. m. of an oxidizing gas consisting of 50% oxygen and 50% nitrogen, were introduced per hour into a mixing vessel. The mixing vessel was provided with a stirrer and a cooling jacket. The'method of working was the same as that described in Example 1. 3.9% of acetaldehyde (about 0.4 kg.

per hour) were again recovered unaltered and 1 again returned to oxidation. A 96% acetic acid with a yield of 98% of the theoretical amount was obtained, the yield of production amounted to 313 kg. of acetic acid per day. Fro m the examples it can be seen that the yield is substantially greater with the use of oxidizing gases rich in oxygen. Calculated on the same volume with the use of an oxidizing gas containing 50% oxygen instead of air, there is obtained nearly three times the production yield.

I claim:

-1. In a process for the continuous production of acetic acid by oxidation of acetaldehyde in the liquid phase with oxygen, the step which consists in continuously introducing at the same time the intimate contact is produced by mechanical mixing.

3. A process according to claim 1 consisting in carrying out the oxidizing process at an absolute pressure of substantially 1.5 atmospheres.

4. A process according to claim 1 consisting in treating the waste 'gases from the acetic acid formation process with acetic acid for the purpose .of recovering acetaldehyde.

5. A process according 'to claim 1 consisting in treating the waste gases with acetic acid at an increased pressure of substantially 1.5 atmospheres absolute.

6. A process as set forth in claim 1 which consists' in introducing continuously into the reaction vessel 9. quantity of oxygen which is at least 1,oss,sse

6 cess of at least 50% over the amount theoretically necessary for the reaction.

7. Process for the uninterrupted production of acetic acid consisting in continuously introduc ing acetaldehyde in the liquid phase into a mix-' 10 ing vessel, and at the same time continuouslyintroducing oxygen in quantities which considerably exceed the quantities theoretically required for the oxidation of all the inflowing acetaldehyde to iorm acetic acid while causing intimate contact oxygen being present in such excess that the efiiuent waste gases issuing from the mixing vessel contain free oxygen.

8. A process for the uninterrupted production or acetic acid, consisting in continuouslyxintroducing acetaldehyde in the liquid phase into a mixing vessel, simultaneously, continuously introducing oxygen in quantities which considerably exceed the quantities theoretically required for the oxidation of all the inflowing acetaldehyde .to acetic acid while causing intimate contact between the acetaldehyde and the oxygen, the quan-.

tity of oxygen being present .in such excess that the'waste gases evolved in the reaction contain ir'ee oxygen, and then passing the said waste gases through cooling and absorption devices for the purpose of recovering unaltered acetaldehyde. "9. Aprocess for the uninterrupted production of acetic acid consisting in continuously introducing acetaldehyde in the liquid phase into a mixing vessel simultaneously, continuously adding oxygen in quantities considerably exceeding those required for the oxidation of all the inflowing acetaldehydeto acetic acid while causing intil 40 mate contact between the acetaldehyde and the oxygen,.the quantity 01' oxygen being present in such excess that the eiiiuent waste gases contain iree oxygen, and then treating the said waste gases with unrectifled acetic acid formed in the reaction vessel, for the purpose of recovering the acetaldehyde.

between the acetaldehyde and the oxygen, the g 10. A process for the uninterrupted production 01' acetic acid, consisting in continuously introducing acetaldehyde in the liquid phase into a mixing vessel, simultaneously, continuously adding oxygen in quantities considerably exceeding the quantities theoretically required for the oxidation of all the inflowing acetaldehyde to acetic acid while causingintimategontact between the acetaldehyde and the oxygen the quantity of oxygen being present in such excess that the 35 eflluent waste gases contain tree oxygen, and then treating the said waste gases first with unrectiiled acetic acid'and then with rectiiied acetic acid for the purpose of recovering acetaldehyde;

,of removing acetic acid.

12. A process for the uninterrupted production of acetic acid consisting in continuously introducing acetaldehyde in the liquid phase into a mixing vessel, and at the same time continuously introducing oxygen in quantities which considerably exceed the quantities theoretically required for the oxidation in the liquid phase of ,all the in-flowing acetaldehyde to form acetic acid, while causing intimate contact between the acetaldehyde and the oxygen the quantity of oxygen being supplied in such excess that tree oxygen is 11 present in the waste gases issuing from the mixing vessel.

- KARL WIESLER.

11. A process for the uninterrupted production i 

